AGATE 


Physical Properties and Origin 


BY 
OLIVER C. FARRINGTON 


CURATOR OF C.wOLOGY 


Archaeology and Folk-lore 


BY 
BERTHOLD LAUFER 


CURATOR OF ANTHROPOLOGY 


— 


NATURAL 
Sa 


fic aoe A Cee Tieramveenrt gh 


ae poh se ests tt 
‘A, FOUNDED BY MARSHALL FIELD QZ 


GEOLOGY 


LEAFLET 8 


FIELD MUSEUM OF NATURAL HISTORY 
CHICAGO 
1927 


LIST OF GEOLOGICAL LEAFLETS ISSUED TO DATE 


No. 1. Model of an ArizonaGold Mine. . . . . . $.10 
No. 2. Models of Blast Furnaces for Smelting Iron ) 
No. 3. Amber—Its Physical Properties and 
Geological Occurrence . . . . 
4.) Meteorites iis i Vins ccaie (Bee age 
5. SOUS Speier cae eae ede he 
6. Lhe Mloone pea: By Ma sey dbra agg SeyS 
No. 7. Early Geological Easton of Chicago . . 
3 
9 


. . . . . . 


Apale reuse inelitens cimohtes un ei ie 
Me HownoldvarevHossilsanetsae | ee wens 


FIELD MUSEUM OF NATURAL HISTORY 
CHICAGO, U.S.A. 


LEAFLET 8. PLATE |. 


“FORTIFICATION’’ AGATE. URUGUAY. 
ARTIFICIALLY COLORED. 


FIELD MUSEUM OF NATURAL HISTORY 
DEPARTMENT OF GEOLOGY 
CHICAGO, 1927 


LEAFLET NUMBER 8 


Agate—Physical Properties and Origin 


Agate is a variety of chalcedony chiefly distin- 
guished by its banded or variegated structure and col- 
oring. Its banded appearance is due to the fact that 
it is made up of a great number of exceedingly thin 
layers which appear as bands in cross section. As 
seen by the naked eye, these bands differ considerably 
in width, some seeming no wider than a line, while 
others may be a quarter to a half inch wide. In real- 
ity, all these bands are made up of still finer ones, the 
individuals of which can be seen only with a micro- 
scope. In a section of agate only one inch in thick- 
ness, Sir David Brewster counted 17,000 such individ- 
ual bands, and this number is probably representative 
of their abundance in most agates. In all agates the 
layers are composed of minute fibers or microscopic 
crystals standing at right angles to the course of the 
bands. Agate is generally semi-transparent rather 
than opaque but the layers may differ considerably in 
this respect and some be quite opaque. These differ- 
ences in translucency correspond to variations in por- 
Osity, as is shown by the fact that whereas the trans- 
lucent layers absorb coloring matters readily, the 
opaque layers are little penetrated by them. As to the 
average size of these pores in agate, it is known that 
the diameter of the pores of water-rich silica colloids 
(jellies) is about one five-millionth of a millimeter, 
and those of agate (which is silica without water) 


[105 ] 


2, FIELD MUSEUM OF NATURAL HISTORY 


are probably smaller, as removal of the water tends 
to contract them. The pores of agate are too small 
to admit the absorption of large molecules like those 
of sugar or they admit them only with difficulty. This 
is shown by the fact that in the process of coloring 
agates black by means of a sugar solution and sul- 
phuric acid, from two to three weeks are required for 
the large sugar molecules to penetrate the agate, while 
only a few hours are necessary for the absorption of 
the smaller molecules of sulphuric acid. 

Owing, probably, to the fibrous structure and dens- 
ity of agate, it is tough and remarkably resistant to 
wear. It is somewhat harder than quartz. These qual- 
ities make it useful for many industrial purposes. 
Chemically, agate is pure silicon, the commonest com- 
ponent of the earth’s crust. Of agates it may be said 
more truly than of other minerals, perhaps, that each 
individual is unique; one does not duplicate another. 
But although agates vary greatly in pattern and in 
color, yet they fall into certain natural groups based 
chiefly on pattern, which permit them to be given 
a certain mineralogical classification. 

The most common and characteristic form of 
agates is one which in cross section resembles an old- 
time bastion, a defensive work characterized by curv- 
ing contours and salient angles. Agates of this pattern 
are known as “fortification” agates (Plate 1). Those 
agates in which the bands run approximately straight, 
are known as “ribbon” agates. This kind of band- 
ing is also characteristic of onyx and hence agates 
of this kind are sometimes known as “onyx” agates. 
Both patterns can sometimes be seen in the same 
agate (Plate IV). If the bands lie so close together 
that a ray of light in passing through them is broken 
up into prismatic colors, it distinguishes what are 
called “rainbow” agates. If the agate is irregularly 


[ 106 ] 


“STVNVO SONVY LNA Ga3SOddNS DNIMOHS JSLVDSV ..NOILVOISILYOS,, 


“Il 3LW1d sc SEE RENE fa 


AGATE—PHYSICAL PROPERTIES AND ORIGIN 3 


and obscurely colored, it is called a “clouded” agate. 
In the so-called ‘‘eye” or “ring” agates the bands run 
in concentric circles. Agates made up of fragments 
of former agates cemented together are known as 
“ruin’’ agates (Plate IV). Characteristic agates of 
this kind are found in Schlottwitz, Saxony. Agates 
appearing to be made up of tubes or pipes cemented 
together are known as “pipe” agates. An important 
variety of agate is that known as “moss” agate, in 
which, as the name indicates, the agate has the ap- 
pearance of containing inclusions of moss (Plate V). 
These inclusions are often arranged in such a manner 
as to give the appearance of a miniature landscape, 
in which case they are known as “landscape” agates 
(Plate VI). 


Agates are generally formed in cavities in volcanic 
rocks. In the escape of gases and vapors from such 
rocks on cooling, cavities similar to those seen when 
pasty substances are heated are often formed and re- 
main open when the rock has cooled. The cavities 
are usually spheroidal in form or, more specifically, 
are often shaped like an almond, whence the term 
amygdaloidal, from the Greek word for almond, is ap- 
plied to them. The size of these cavities is also often 
about that of the almond but they may be much larger. 
It is in cavities like these that agates are chiefly 
formed, occurring as a filling that takes the shape of 
the cavity. Being of very tough material, which re- 
sists both physical and chemical corrosion, the agate 
nodules (the lumps or masses formed by the filling of 
the cavities) are usually left intact after the rock 
about them has decomposed and hence agates are 
often found in soil or in beds of streams. In the lat- 
ter case they may occur far removed from the place 
of their origin. The size of the agate nodules varies 
according to the size of the cavity in which they are 


[ 107] 


4 FIELD MUSEUM OF NATURAL HISTORY 


formed. From very minute, they run up to weights as 
high as 4,000 pounds. 

Although most agates are formed in the cavities 
of volcanic rocks, some are formed in other cavities, 
such, for instance, as those left by the decay of wood. 
The siliceous linings of rock fissures sometimes also 
have the structure of agate. The so-called agate nod- 
ules are not always composed entirely of agate. Fre- 
quently, quartz crystals or other forms of quartz or 
even other minerals line the interior of the nodules, 
or are interpolated with the layers. 


OCCURRENCE OF AGATES 


Agates are found in many parts of the world, be- 
ing likely to be formed wherever there are trap’ rocks. 
As already noted, decay of these rocks leaves the more 
resistant agate nodules in the soil, from which they 
are often distributed by streams. 

Agates resulting from the decomposition of the 
trap of the Deccan plateau in India have been gathered 
for thousands of years. After more or less fashioning 
by native lapidaries they have found their way to Eu- 
ropean and Oriental markets. A further description of 
this industry will be found in subsequent pages. The 
principal European locality for agates is in south- 
western Prussia in the region of the Nahe River, a 
tributary of the Rhine. Not only has the agate found 
in this region been worked for centuries, but the vari- 
ous processes of shaping and coloring it, have been so 
fully developed there that it is now the world center 
of the agate business. Among other European locali- 
ties, the so-called Scotch pebbles from Forfarshire 
and Perthshire in Scotland furnish attractive agates. 

The most extensive ocurrence of agate known at 
‘Trap. A common name for any dark, finely crystalline, ig- 

neous rock. 
[ 108 ] 


LEAFLET 8. PLATE 


AGATE-LIKE BANDING PRODUCED BY DIFFUSION IN GELATINE. 
*"LIESEGANG’S RINGS’’ 


AGATE—PHYSICAL PROPERTIES AND ORIGIN 5 


the present time is in the mountain chain extending 
from Porto Alegre, State of Rio Grande do Sul, in 
Brazil, to the district of Salto in northern Uruguay. 
The agates of this region surpass in size and beauty 
any others known and they form at the present time 
the principal source of supply of agates for commer- 
cial purposes. 

A portion of the agate-bearing area in Uruguay 
was visited in 1926 by Associate Curator H. W. Nich- 
ols of the Museum on the Captain Marshall Field 
South American Expedition of that year. Mr. Nichols 
reports that the agates are dug from shallow pits in 
grazing lands, where they occur in considerable quan- 
tity. Associated with the agates are many hollow 
stones which are often lined with amethyst crystals. 
Some of these are of gem quality. Pieces of agate are 
also found in the stream beds of the region, fresh sup- 
plies being brought down by floods. The largest dig- 
gings at present are in the Catalan district of Artigas, 
Uruguay, which is about one hundred miles north of 
Salto. 

Agates of considerable beauty, though not of great 
size, are found in many places in the United States. 
Those of Agate Bay, Lake Superior, have rich colors 
and make attractive charms and other ornaments. 
Agates are found in the beds of many streams in 
Colorado, Montana and other regions of the Rocky 
Mountains. They occur all along the Mississippi River, 
especially in Minnesota, also along the Fox River in 
Illinois, in the trap rocks bordering the Connecticut 
River and on the coasts of California and Oregon. 


METHOD OF FORMATION OF AGATE 


No one who gives much consideration to the sub- 
ject of agates, can fail to be impressed with the difficul- 
ty of explaining how they are formed. They appear to 


[109 ] 


6 FIELD MUSEUM OF NATURAL HISTORY 


be made up of successive layers deposited on the walls 
of the interiors of cavities, each layer toward the in- 
terior being younger than the one preceding. Some- 
times the process of deposition appears to have con- 
tinued until the cavity was entirely filled, but in other 
cases a vacancy still remains at the center. If the 
above is the method of formation, it is difficult to un- 
derstand why the deposition of the first layer, or, at 
least of the first two or three layers, would not close 
the cavity to succeeding deposits. 

Various attempts have been made to answer this 
question. Haidinger, a German geologist, writing 
about 1849, made the suggestion that the moisture 
ordinarily found in rocks, the so-called “‘mountain 
moisture” would “sweat” through into the cavities and 
that successive solutions of silica would thus enter 
through diffusion. This explanation seemed adequate 
to many investigators, but others have agreed with 
Noggerath, a contemporary of Haidinger, that it is 
doubtful if solutions would continually enter the cavity 
in this manner, especially as the outer layers of agate 
nodules are known by agate cutters to be particularly 
hard and impervious to liquids. As a better explana- 
tion Noeggerath called attention to an apparent canal 
or conduit which can be seen leading outwards from 
the interior of most agates and which he believed re- 
mained open during the formation of the agate for the 
admission of percolating waters. Such a channel is 
shown in Plate II. In some agates several such so- 
called entrance canals are to be seen, but in some, 
unfortunately for the theory, none can be found. 
Moreover, it is difficult to understand why such canals, 
if they ever existed, would remain open. The above 
theories, however, are the only ones that until recently 
have seemed at all worthy of credence as possible ex- 
planations of the manner of formation of agates and 


[ 110 ] 


LEAFLET 8. PLATE IV, 


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es 
at: 
» 


‘“FORTIFICATION’’ AGATE WITH LAYERS IN TWO DIRECTIONS. 


“*RUIN’’ AGATE. 


AGATE—PHYSICAL PROPERTIES AND ORIGIN if 


for many years were accepted by most investigators. 
The theory is stated by Bauer in a complete form as 
follows: ‘To explain this phenomenon [the forma- 
tion of agates] the existence is assumed of hot, inter- 
mittent springs, such as are now seen to perfection 
in the geysers of Iceland and in the United States 
National Park on the Yellowstone River. The essen- 
tial condition is that the hot or warm water rising 
up from the depths shall saturate the rocks, and that 
it shall sink again, leaving the rocks dry for a period. 
The hot water dissolves out the silica and other con- 
stituents of the rock and the solution fills up the 
amygdaloidal cavities. When the waters sink, these 
cavities are emptied, only a film of water covering 
their walls being left behind. On the evaporation 
of this film, which readily takes place at such a high 
temperature, a thin layer of silica is deposited on the 
walls of the cavity. When the hot spring again rises, 
the same thing takes place and a second layer of silica 
is deposited, and so on, until the cavity is more or less 
completely filled up. Each time, the fluid passes into 
and out of the cavity by the canals, which are for 
this reason often referred to as tubes of entry or 
escape. The fluid, also, perhaps, passes to a certain 
extent through the porous agate itself. Crevices, fis- 
sures, and other cavities in the rock are, of course, 
filled with agate in the same way.” 

It is only recently that a theory for the formation 
of agates has been proposed which gives a totally 
different explanation from the above and which is in 
many respects more satisfactory than the earlier views. 
According to the later theory, the rock cavity in which 
the agate is formed, first becomes more or less filled 
with silica in a colloidal (jelly-like) condition. In such 
a colloid a banded structure can be produced by proc- 
esses which can be illustrated with ordinary gelatine. 


Eah ey) 


8 FIELD MUSEUM OF NATURAL HISTORY 


The following experiment as described by Ostwald 
in 1896 illustrates this process. If silver nitrate is 
introduced into a colloid which contains ammonium 
bi-chromate, silver chromate (a red salt) is at once 
formed, but it does not at first appear in a solid form. 
It is still dissolved. Gradually, however, through the 
continual formation of silver chromate, the solution 
becomes so concentrated that it must somewhere sep- 
arate out. This separation takes place first at an edge. 
Then all the super-saturated substance makes its way 
to this edge and likewise separates out. An essential 
consequence of this is that adjacent to this deposit 
a zone is formed which is free from silver chromate. 
But this zone also does not contain ammonium bi- 
chromate, for this has been used up by the silver ni- 


Ir g 


Fig. 1. Origin of banding in colloids. 

trate. Here, then, no new silver chromate can form 
and the zone becomes colorless. The excess of silver 
nitrate pushes on, however, and by the same reactions 
forms a second band of silver chromate and a color- 
less zone. Continuation of this process gives a banded 
structure. 

The process is illustrated diagramatically in Fig. 1. 
The areas colored yellow represent a mass of gelatine 
which contains ammonium bi-chromate. In a, the 
light-red area at the top represents a zone of dis- 
solved silver chromate. In b, the dark-red edge shows 


[112] 


LEAFLET 8. PLATE V. 


MOSS AGATE. CHINA. 


IMITATION OF MOSS AGATE. 
PRODUCED BY ADDING IRON VITROL TO WATER GLASS. 


Coe 


Imitation of Moss Agate. The word 


“vitrol’’ should read ‘‘vitriol.’’ 


ERRATUM—Plate V. 


U} 


AGATE—PHYSICAL PROPERTIES AND ORIGIN 9 


the beginning of the formation of a zone of precipi- 
tated silver chromate. To the neighborhood of this 
zone as shown in ¢, all the super-saturated silver 
chromate wanders, leaving a colorless area. But be- 
low the chromate-free area a new zone of dissolved 
silver chromate has formed as shown in d. Ere this 
has had time to pass to the zone of deposit, its con- 
centration has become so high that within its own area 
deposition takes place as shown in e. By the gather- 
ing of the super-saturated silver chromate at this edge, 
a second, colorless zone is formed as shown in f. Sim- 
ilarly, a third zone of deposit is formed as shown in g 
and so the process goes on until a series of bands is 
produced. These bands are parallel to the original 
outline of the colloid and are of wonderful regularity. 
Their appearance is marvellously like that of the bands 
of a fortification agate. An example of banding pro- 
duced in this way is shown in Plate III. 

Besides explaining the banding, this view of the 
method of formation of agates also indicates why agate 
nodules are often hollow in the interior. Drying of 
the colloidal silica causes a shrinking in bulk which 
would often leave such a hollow. The theory also 
explains the frequent occurrence of quartz crystals at 
the interior of agates. Crystals cannot form in col- 
loids on account of surface tension, but when the ten- 
sion is relieved at the hollow interior of the nodule, 
complete crystallization can take place there. 

Anyone wishing to illustrate for himself the for- 
mation of the bands referred to can readily do so by 
making the following experiment: Dissolve 3 grams 
of gelatine in 60 c. c. of water, add 3 drops of a 5% 
citric acid solution and 4 drops of a 10% ammonium 
bi-chromate solution. Stir the liquid and pour some 
of it on a clean glass plate. Allow it to harden for 
one to two hours. Then with a glass rod that has been 


[ 113 ] 


10 FIELD MUSEUM OF NATURAL HISTORY 


dipped into a 25% solution of silver nitrate draw a 
band of silver nitrate about the outer edge of the gela- 
tine. Put the plate in a cool, dry place not exposed 
to sunlight and watch the course of the reaction. 
Gradually the silver nitrate will penetrate the gela- 
tine and the formation of bands of silver chromate 
will begin. The process will continue and bands be 
formed for 24 to 48 hours or until the silver nitrate 
and ammonium bi-chromate have exchanged positions, 
the silver nitrate ultimately reaching the center of 
the plate and the ammonium bi-chromate the circum- 
ference. 

The formation of bands of this sort was first made 
known by a German chemist, Raphael Ed. Liesegang, 
and the phenomenon is now generally known as “‘Liese- 
gang’s rings.” The width of the bands and other 
features can be varied by using other percentages of 
chemicals than those given here and other chemicals. 
Then too, by varying the points of application of the 
silver nitrate or by introducing it as drops or lines, 
imitations of other patterns seen in agates can be 
obtained. 

According to the present view, then, fortification 
or common agates originate from a filling of hollow 
spaces in rocks by a silica colloid (jelly), within which 
an iron compound has been rhythmically deposited. 

Although the banding of fortification agates can 
be acceptably explained by the introduction of iron 
salts into colloidal silica, it is at first sight difficult to 
see how moss and pipe agates and some other forms 
can be accounted for in this way. 

For a long time and even in mineralogical text 
books up to the 19th century it was thought, and stated, 
that moss agates were made up of moss enclosed in sili- 
ea. Peculiar enclosures in some other kinds of agates 
were also explained as petrifications of other once living 


[114] 


12 FIELD MUSEUM OF NATURAL HISTORY 


In this way the forms known as pipe agates are sup- 
posed to originate. 


NATURAL COLORS OF AGATES 


While the majority of agates are colorless in their 
natural state, some natural colors do occur. Red and 
brown are the most common and are due to a content 
of iron oxide. If the color is brown, iron hydroxide 
is the coloring matter, if red, iron oxide. The red 
color is usually produced by alteration of the brown, 
loss of water by exposure to sun’s heat forming the 
oxide from the hydroxide. In agates with straight 
bands these colors form the layers of sard and car- 
nelian so much used for cameos. Another color na- 
turally occurring is black. It rarely occurs massive, 
usually appearing as scattered flakes. Oxidation often 
causes this to change to red or brown, usually in spots 
or along clefts. Green is a color often seen in the moss 
agates and adds to the impression that these agates 
contain real moss. It is now well known, however, 
that the moss-like appearance is not due either in color 
or form to moss. As already noted, green, fibrous in- 
clusions can be produced in water-glass, the colloidal 
form of silica, by introducing iron vitriol. Thread- 
like and moss-like forms may then appear as shown 
in Plate V. Whether the green fibers of moss agates 
are of this nature or consist of some fibrous mineral 
such as hornblende or chlorite is not certain. Perhaps 
both modes of origin occur. 


ARTIFICIAL COLORING OF AGATES 


Nearly all agates that one sees in use nowadays 
have been artificially colored. While the possibility of 
coloring agates artificially has been thought to have 
been known to the Romans, and as having been men- 
tioned by Pliny, it is shown by Dr. Laufer in the later 


[116] 


BEAGLE S: PLATE VII. 


SECTION OF AGATE. 


SHOWING NATURAL COLOR AT THE UPPER END AND ON THE REMAINDER 
VARIOUS ARTIFICIAL COLORS. 


AGATE—PHYSICAL PROPERTIES AND ORIGIN 13 


pages of this leaflet that this view is incorrect. At any 
rate modern methods of coloring agates were not intro- 
duced until 1819, when a method of coloring black was 
accidentally discovered in Germany. Production of a 
red color by burning was to be seen in nature, since 
one could there observe that portions of agates pro- 
truding from the earth were reddened as compared 
with the covered portions. This natural process was 
at first imitated by exposing agates to the heat of the 
sun, but later the same result was obtained more 
quickly by heating the stones in ovens. It being 
found, however, that some stones would not color in 
this way, it was concluded it was because they con- 
tained no iron compounds. Accordingly experiments 
were made to introduce iron compounds into the stones, 
and the colors were then successfully obtained. Hav- 
ing succeeded in this, the production of other colors 
was sought. In 1845 a method of coloring blue was 
discovered and in 1853 one of coloring green. Dreher 
in his book on the coloring of agates gives the follow- 
ing table of colors which can be produced in agates 
and the methods of producing them :— 


DESIRED COLORING HOW 
COLOR MATTER OBTAINED 

Red Iron oxide From iron nitrate by heating. 

Bluish-green Chromic oxide From chromic acid or am- 
monium  bi-chromate’ by 
heating. 

Apple-green Nickel oxide From nickel nitrate by heat- 
ing. 

Brown Caramel From sugar by strong heat- 
ing. 

Blue Berlin blue From yellow prussiate of 
potash and iron vitriol. 

Blue Turnbull’s blue From red prussiate of pot- 


ash and iron vitriol. 


Black Carbon From sugar and _ sulphuric 
acid. 


[117] 


14 FIELD MUSEUM OF NATURAL HISTORY 


The methods of coloring depend upon the absorp- 
tion in the pores of the stone of some substance which, 
when acted on by another chemical or by heat, will 
give the color desired. Inasmuch as the layers of 
agate differ considerably in their porosity, there are 
corresponding variations in the amount of color they 
will absorb. This gives pleasing variety to the color 
effects. The agate colorists call layers which have 
great porosity and hence absorptive capacity, “soft,” 
while those so compact that they take little or no color 
are called “hard.” 

For successful coloring, the stone must first be 
freed from any substances which would prevent the 
entrance of coloring matter into the pores. Thus, all 
oils or fats must be removed, as well as iron or other 
oxides of an undesirable color. Soaking in caustic 
soda solution will remove the fatty substances and 
treatment with nitric or hydro-chloric acids undesir- 
able iron compounds. For the latter process the stone, 
according to Dreher, should be placed in warm acid 
for two or three days, and the acid be finally brought 
to boiling. After cooling and washing, the operation 
should be repeated several times until the pores of the 
agate are thoroughly cleaned. 


For coloring red, a solution of iron nitrate is used. 
This is generally prepared, according to Dreher, by 
adding to about half a pound of iron nails, about four 
times their weight of concentrated nitric acid. A 
more or less slimy mass which is produced is allowed 
to settle and the clear liquid poured off, this procedure 
being repeated several times until the liquid has be- 
come perfectly clear. The stones or sections desired 
to be colored are immersed in this liquid at a luke- 
warm temperature and allowed to remain for a time 
determined by their thickness. Stones 3 millimeters 
thick, it is said, should remain 2 to 3 weeks, those 10 


[118 ] 


AGATE—PHYSICAL PROPERTIES AND ORIGIN 15 


millimeters thick, 3 to 4 weeks. Stones thicker than 
this can rarely be colored throughout. For the best 
results repetition of the treatment is recommended, 
the stone being dried after the first bath and then re- 
immersed. The agate is now saturated with iron 
nitrate and this must be changed to iron oxide by 
strong heating. First the stone is dried at a gentle 
heat, the time required being from two to ten days, 
according to the thickness of the stone. Then, with- 
out being allowed to cool, it is put in a closed crucible 
on a warm hearth and heated until the hearth be- 
comes red hot. It is then allowed to cool very slowly, 
care being necessary both in heating and cooling, that 
no sudden change of temperature will occur which 
would fracture the stone. 

For coloring green, as much chromic acid or potas- 
sium bi-chromate as possible is dissolved in a quart of 
water. The stone desired to be colored is placed in 
this bath and if thin, allowed to remain from one to 
two weeks, according to the degree of absorption. 
Stones one-half inch in thickness often must remain 
two months before they absorb sufficient liquid. When 
this treatment is finished the stone is placed in a 
closed, flat vessel containing lumps of ammonium car- 
bonate. It is then allowed to remain exposed to the 
fumes of this volatile substance for about two weeks. 
It is then dried and gradually and strongly heated 
until the desired color is obtained. 

For coloring black, about 18 ounces of sugar are 
dissolved in a quart of water and the stone allowed 
to remain in this solution for from 2 to 3 weeks, ac- 
cording to its absorptive capacity. Water must be 
added from time to time during the immersion of the 
stone in order to replace that lost by evaporation. 
The stone is then transferred to a vessel containing 
concentrated sulphuric acid and then slowly warmed 


{119 ] 


16 FIELD MUSEUM OF NATURAL HISTORY 


for about an hour. The acid is then brought to boil- 
ing for from 15 to 20 minutes or, in some cases, 1 to 
2 hours. This latter operation must be carried on with 
considerable care, owing to the poisonous nature of 
fumes given off by the acid and the explosive action 
which occurs if water comes in contact with it. If 
one wishes to avoid boiling the acid, the desired effect 
can be obtained by allowing the stone to remain in 
warm acid for an hour, then cooling and warming it 
again for an equal length of time. Owing to the 
strong affinity which sulphuric acid has for water, the 
acid remaining in the stone will generally cause it to 
become moist after it has been removed from the acid. 
Drying the stone 1 or 2 days or immersing it for 5 or 
6 hours in cold water and then drying it at a moder- 
ate temperature will remove this tendency to “‘sweat.” 


For coloring blue, a solution is made of 9 ounces of 
yellow prussiate of potash (potassium ferro-cyanide) 
in a quart of water. In this lukewarm solution the 
stone to be colored is left for from one to two weeks, 
according to its absorptivity. After being well washed, 
the stone is then put into a solution of iron vitriol 
(ferrous sulphate) made by adding to a quart of water 
as much of the iron vitriol as will dissolve. Left in 
this for 8 to 10 days the stone is then removed, well 
washed and dried slowly. If a satisfactory color has 
not been obtained, the stone can be returned to the 
vitriol bath until the desired shade is reached. A 
dark blue is produced by a few drops of sulphuric 
and a few of nitric acid added to the iron vitriol solu- 
tion, or red prussiate of potash (potassium ferricya- 
nide) can be used instead of the yellow prussiate of 
potash for the first solution. The blue coloring is 
much used to imitate lapis lazuli, the so-called German 
or Swiss lapis being artificially colored chalcedony or 
agate. 


[ 120] 


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AGATE—PHYSICAL PROPERTIES AND ORIGIN 17 


The methods above described will indicate the 
principal ones used in coloring agates. By modifications 
of these methods other colors can be obtained. Ani- 
line dyes can be used, but they are likely to fade in 
a short time. An illustration of a number of colors 
artificially given to a single section of agate is shown 
in Plate VII. 

The coloring of agate, like the cutting of agate, is 
carried on chiefly in Germany. In the localities de- 
voted to this industry it is said to be to a considerable 
extent a household occupation, the processes often 
being carried on in home kitchens. 


CUTTING AND POLISHING OF AGATES 


The industry of cutting and polishing of agates is 
now carried on chiefly in the vicinity of Idar and 
Oberstein, two towns located on the Idar and Nahe 
rivers in southwestern Germany. Agates were form- 
erly abundant in this region and the art of cutting 
and polishing them was developed to such an extent 
that when the local supply of agates was exhausted 
they were sent there from other localities. 

That activity in this line began at a very early 
period we know from accounts of it which were given 
as early as the year 1497. Subsequently the industry 
declined, owing to the depletion of local supplies of 
agate, but the discovery of the Brazilian material re- 
vived it with great vigor and nearly all modern agate 
cutting, coloring, engraving, etc., is now done in this 
region. 

In carrying on this work, the rough agates are first 
broken with hammer and chisel into shapes approxi- 
mating those desired. These pieces are then some- 
what further shaped on metal wheels charged with 
emery or diamond powder, or they may be ground at 


[ 121] 


18 FIELD MUSEUM OF NATURAL HISTORY 


once on great sandstone wheels. These wheels are 
often 5 feet in diameter. They contain grooves of dif- 
ferent shapes which fit the various forms of agates. 
Grinding of the agates to desired shapes is performed | 
by workmen who lie prone upon a sort of hollow bench 
and, bracing their feet against cleats nailed to the floor, 
force the agates with the pressure of their whole bodies 
against swiftly revolving grindstones (Plate VIII). 
Many of the grindstones are wide enough so that 
two workmen can use the same one at one time, 
one on either side. The agates usually emit a bright, 
phosphorescent light in the process of grinding. The 
stones are kept constantly wet with a stream of wa- 
ter. Both for this reason and for the water power 
needed, the mills in which this work was done were 
formerly all located on the banks of streams. At the 
present time, however, steam and electrical power and 
other modern methods are employed. Vases, bowls 
and such objects are hollowed out by special grind- 
stones, as much advantage as possible being taken of 
the natural contours of the agates. After being ground 
to the desired shapes, the articles are polished, this 
work being done on wooden wheels to which suitable 
polishing powders are applied. This work can be done 
by women and children. Owing to its hardness and 
toughness agate takes a high and durable polish. Be- 
cause of its hardness, toughness and capacity for high 
polish, as well as its pleasing patterns and colors, 
agate has a number of uses in which ornament is com- 
bined with utility. Thus it is made into pen holders, 
handles for dental and surgical instruments, umbrella 
handles, match boxes and toilet cases. Agate bearings 
are of the highest utility for chemical and other bal- 
ances and no chemical laboratory is complete without 
one or more agate mortars. For ornamental purposes 
agate serves for cameos and other stones for breast- 


[ 122 ] 


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AGATE—PHYSICAL PROPERTIES AND ORIGIN 19 


pins, for hair-pins, ear-rings, watch charms, sleeve 
buttons, necklaces, bracelets and rings, especially seal 
rings (Plate XI). 

It is much prized by many semi-civilized peoples, 
especially those of Africa, for ornamental purposes, 
and the late Dean C. Worcester once told the writer 
that it was one of the most desired objects of barter 
in demand among the Filipino peoples. 

The engraving of agate, especially to produce cam- 
eos and intaglios, is an art which has come down to 
us from early times and was principally cultivated by 
the Greeks and the Romans. In addition to the artis- 
tic excellence of the engravings, many of the early 
works show great skill in using the different color- 
ings of the agate for decorating the figures. Ex- 
amples of such a use of agate are shown in the cameos 
of Plate XII. 


Agate was long used as the birthstone for June, 
but it is now largely superseded in that month by the 
pearl. The verse which accompanied the use of agate 
was :— 

Who comes with summer to this earth, 
And owes to June her hour of birth, 

With ring of agate on her hand 

Can health, wealth and long life command. 

In Hall 34 on the second floor of the Museum in a 
case near the east entrance, varieties of agate and 
their natural and artificial colorings are illustrated by 
specimens. Other specimens are shown in the same 
hall in their systematic order in the mineral collection, 
and in Higinbotham Hall some of the choicer speci- 
mens used especially for jewelry may be seen. 


OLIVER C. FARRINGTON. 


[ 123 J 


Agate—Archaeology and Folk-lore 


The Sumerians, the earliest inhabitants of Meso- 
potamia, were the first nation in history, as far as we 
know at present, that recognized the ornamental value 
of semiprecious stones and that understood and prac- 
tised the art of stone-cutting for the purpose of mak- 
ing cylinder seals, signet-rings, beads, and other arti- 
cles of jewelry. In the excavations undertaken by 
Field Museum at Kish in cooperation with Oxford 
University under the auspices of Captain Marshall 
Field, great quantities of beads of various substances 
and forms have been brought to light. These beads 
were worn by both sexes, and the materials commonly 
used for their manufacture were agate, carnelian, and 
lapis lazuli, which occur in almost every necklace. It 
appears from their relative number that carnelian and 
agate beads were more popular than those of lapis 
lazuli. Many are of oblong, cylindrical shape, up to 
two and two and a half inches long with perforations 
firmly and evenly drilled. Many examples of such 
beads may be viewed in the exhibits of Kish antiquities 
in Stanley Field Hall (Cases 6 and 20). In Plate XIII 
one of the finest necklaces from Kish is reproduced. 
It consists of agate and lapis-lazuli beads alternating, 
and also contains beads of gold foil made of the same 
shape as those of agate. Perrot and Chipiez figure 
a cylinder of veined agate on which are portrayed 
winged quadrupeds seizing and devouring gazelles. 
It was found by De Sarzec at Tello, and is now in the 
Louvre of Paris. The source of the agates and car- 
nelians used by the Sumerians has not yet been traced. 

Aside from beads, the Sumerians used agate also 
for making ceremonial axe-heads. One of these, with 
a three-line inscription, is in the American Museum 


[ 124 ] 


LEAFLET 8. PLATE XI. 


MAKING AGATE BEADS. 
IDAR, GERMANY. 


AGATE—ARCHAEOLOGY AND FOLK-LORE 7A | 


of Natural History, New York, and is dated by J. D. 
Prince between 3000 and 2300 B.c., probably nearer 
the former than the latter date. It is illustrated and 
described in Journal of the American Oriental Society, 
XXVI, 1905 (pp. 93-97), also in Bulletin of the Ameri- 
can Museum of Natural History, XXI (pp. 37-47). 
Another Babylonian axe-head of agate, inscribed with 
characters of an early form, is in the Metropolitan 
Museum of Art, New York. 

Agate is first mentioned in literature by Theo- 
phrastus (372-287 B.c.) in his small treatise On 
Stones. He briefly refers to it as a beautiful stone 
which is sold at a high price, and he derives its name 
from the river Achates in Sicily, where such stones are 
said to have been found for the first time. This ety- 
mology is repeated by Pliny, and has been generally 
accepted by the ancients. A derivation of the word 
from the Semitic has been attempted recently, but is 
not convincing. 


Pliny, in his Natural History, discusses agate to 
some extent, but gives no description of it. He writes 
that ‘““Achates is a stone which was formerly held in 
high esteem, but is not so now; it was first found in 
Sicily, near a river of that name, but has since been 
discovered in numerous other localities.”” We may as- 
sume that because it was found in numerous localities, 
it had lost its former appreciation. Besides Sicily, 
Pliny gives Crete, India, Phrygia, Egypt, Cyprus, the 
Oeta Mountains, Mount Parnassus, Lesbos, Messenia, 
Rhodus, and Persia as places where agate occurred. A 
number of varieties are named by him; such names as 
laspachates (‘‘jasper-like agate’), smaragdachates 
(“emerald agate”), haemachates (“blood agate”), and 
leucachates (“white agate’) apparently refer to color 
varieties, while dendrachates (“tree agate’) alludes 
to the designs in the stone and may correspond to our 


[ 125 ] 


22 FIELD MUSEUM OF NATURAL HISTORY 


moss agate. Corolloachates (“coralline agate’) was 
spotted all over, like sapphirus, with drops of gold, and 
was commonly found in Crete, where it was also known 
as “sacred agate.” It was regarded as capable of heal- 
ing wounds inflicted by spiders and scorpions, a prop- 
erty which Pliny says might really belong to the stones 
of Sicily, as scorpions in that island lose their venom. 
The agates found in Phrygia have no green bands, and 
those of Thebes in Egypt lack red and white veins. 
The Egyptian agate was reputed as an antidote to the 
poison of the scorpion, and the stones of Cyprus were 
credited with the same property. By some people the 
highest value was set upon those stones which present 
a transparency like that of glass. 

Pliny, further, relates a number of superstitious 
notions entertained by the Magi of Persia with refer- 
ence to agates. Stones covered with spots like a lion’s 
skin were believed to be an efficient protection against 
scorpions. In Persia, agates were used, by a process of 
fumigation, for stopping storms and hurricanes, as 
well as the course of rivers; if they were thrown into a 
boiling cauldron and turned the water cold, this prop- 
erty was regarded as a proof of their efficacy. A simi- 
lar notion, it will be seen below, turns up in China. To 
be really efficacious, Pliny adds, the stones must be 
fastened with hair from a lion’s mane; hyena’s hair is 
rejected in this case, as it is apt to arouse discord in 
families. An agate of one color renders the athletes 
invincible, the Magi argue, on the ground that if 
thrown into a jar filled with oil together with pig- 
ments and boiled for two hours, it will impart a uni- 
form color of vermilion to all the pigments. 

In this case, it was not the agate which in the 
opinion of the Magi received new colors, but it was the 
coloring matters which through the agency of agate 
changed all their colors into one—vermilion. And since 


[ 126 ] 


AGATE—ARCHAEOLOGY AND FOLK-LORE 23 


vermilion was the color proclaiming victory, and agate 
had the effect of producing this color in other pigments 
of a different nature, the Magi reasoned that an agate 
carried by an athlete would lead him to victory. The 
question here is not of a technical process, but is 
merely one of a purely imaginary, magical supersti- 
tion. The doctrines of the Magi are frequently quoted 
by Pliny, but as a rule with disapproval. 

Another passage in Pliny’s Natural History has 
been interpreted by some writers as referring to the 
artificial coloring of agates. In fact, however, the 
question here is neither of agates nor of artificial col- 
oring. Pliny in this case speaks not of achates, but of 
cochlides, a word derived from cochlea (‘“snail’’), 
which may refer to shells or, according to others, to 
petrified shells, or to stones of snail-like shape. Pliny 
informs us that cochlides are now very common, being 
rather artificial than natural productions, which were 
found in Arabia in large masses. These, it is said, are 
boiled in honey for seven days and nights uninter- 
ruptedly. By this process all earthy and faulty par- 
ticles are removed; and thus cleaned, the mass is 
adorned by the ingenuity of artists with variegated 
veins and spots, and cut into shapes to suit the taste 
of purchasers. These articles were formerly made of 
so large a size that they were used in the East as 
frontals and pendants for the trappings of the horses 
of kings. 

Pliny, accordingly, speaks merely of purifying a 
certain substance of unknown character in honey, but 
says nothing about new colors being brought out in it 
by means of a chemical process. On the contrary, he 
states expressly that veins and spots were added by 
the hands of artists. Noggerath, a German scholar, 
who was familiar with the artificial coloring of agates 
as practised in Idar and Oberstein, has simply inter- 


[127] 


24 FIELD MUSEUM OF NATURAL HISTORY 


preted this process into the above passage of Pliny, 
and this speculative hypothesis has been adopted by 
many others without reason. There is no evidence 
whatever to the effect that the method of coloring 
agates artificially was known to the ancients, and the 
fact remains that no such agate of classical antiquity 
has ever been found. 


The Physiologus, a very popular Greek natural 
history, which originated at Alexandria in the second 
century A.D. and was subsequently translated into all 
European languages, contains a story about the agate 
and the pearl, which does not occur elsewhere. It is 
said that the divers avail themselves of an agate in 
searching for pearls. They fasten a piece of agate to 
a rope which is let down into the sea. The agate turns 
into the direction of where a pearl is hidden, and re- 
mains there steadfast, so that they find the pearl by 
diving alongside the rope. 

Pliny mentions a valuable agate in the possession 
of Pyrrhus, the king who was so long at war with the 
Romans. On this agate were to be seen the Nine Muses 
and Apollo holding a lyre, not as a work of art, but as 
the spontaneous produce of nature, the veins in the 
stone being so arranged that each of the. Muses had her 
own peculiar attribute. We must confess that either it 
must have required a high flight of imagination to 
recognize these pictures in the veins of this agate, or 
that nature had been considerably aided by art. 

It is not stated by Pliny or other ancient writers 
that agate was cut into gems, but a number of cut 
gems of agate have come down to us, and are preserved 
in museums or private collections. They go back as 
far as the Aegaean or Mycenaean age, agate gems with 
mythological subjects having been discovered at 
Vaphio. A few cameos of agate and carnelian are on 
view in Case 2 (upper left section) of the Gem Room 


[ 128 ] 


AGATE—ARCHAEOLOGY AND FOLK-LORE 25 


(H. N. Higinbotham Hall). Aside from cut gems, 
agate was wrought into beads, scarabs, rings, and 
figures. 

Ointment bottles, cups and bowls were also occa- 
sionally made of agate, but few of these have survived. 
The best known example is a precious agate bowl pre- 
served in Vienna and measuring 2814 inches in di- 
ameter. It was brought to Europe by the crusaders 
after the conquest of Constantinople. Another famous 
agate vessel in existence, presumably made at the time 
of Nero, is a two-handled cup holding over a pint and 
covered with Bacchanalian subjects. It was presented 
by Charles the Bald in the ninth century to the abbey 
of St. Denis, and was used to hold the wine at the coro- 
nation of the kings of France. In the Treasury of 
Vienna there is an agate bowl with a diameter of 30 
inches, which is traditionally believed to have been 
made about A.D. 1204. 

The Persians, Armenians, and Arabs, like all 
Oriental nations, do not clearly discriminate between 
agate, carnelian, chalcedony, and related stones. The 
most esteemed kind is called yamani (“originating 
from Yemen’’), as it is chiefly found in Yemen, but, 
according to Arabic authors, also came from India and 
Maghreb (northwestern Africa). The stone was 
chiefly utilized for finger and signet rings in which 
the wearer’s name was engraved. A verse from the 
Koran or also a magical figure was sometimes carved 
in such an agate which then served as a talisman. It 
was believed that those wearing a yamani ring were 
guarded against the danger of being killed by a col- 
lapsing wall or house. 

From ancient times India has been celebrated for 
the beauty of its agates. Pliny narrates that the agates 
of India possessed great and marvelous properties, as 
they present the appearance of rivers, woods, beasts of 


[ 129] 


26 FIELD MusEUM OF NATURAL HISTORY 


burden, and forms even like ivy and the trappings of 
horses,—alluding to undulated and moss agates. The 
druggists of his time, according to Pliny, used these 
as stones for grinding drugs, and the very sight of 
them was regarded as beneficial for the eyes. Held in 
the mouth, they were believed to allay thirst. 

In the sixteenth century Limodra in Guzerat was 
the principal seat of the agate industry, the mines 
being situated four miles from the town. This locality 
was visited early in the sixteenth century by Duarte 
Barbosa, a Portuguese traveller, who reports, “Here 
is found an agate (alaquequa) rock, which is a white, 
milky, or red stone, which is made much redder in the 
fire. They extract it in large pieces, and there are cun- 
ning craftsmen here who shape it, bore it and make it 
up in divers fashions; that is to say, long, eight-sided, 
round, and olive-leaf shapes, also rings, knobs for hilts 
of short swords and daggers, and other ways. The 
dealers come hither from Cambaya to buy them, and 
they sell them on the coast of the Red Sea, whence they 
pass to our lands by way of Cairo and Alexandria.” 

Barbosa found also that a great amount of work 
was done at Cambay in coral, agate, and other stones. 
In the beginning of the seventeenth century the head- 
quarters of the agate industry appear to have been 
transferred from Limodra to Cambay, in the Bombay 
Presidency. Henceforth only the preliminary opera- 
tions of sorting the stones and exposing them to fire 
to develop their color were performed at Limodra, and 
this is the case even now. They are then taken to Cam- 
bay to be cut, polished, and worked up. 

The Portuguese word alaquequa or alaqueca, also 
laqueca, is derived from Arabic al’ aqiq, and refers to 
the red carnelians exported from India. The Portu- 
guese settled in India called olhos de gato (“cat’s 
eyes’) what is known as Indian eye-stone or eye- 


[ 130 ] 


LEAFLET 8. PLATE XIil. 


CAMEOS MADE FROM AGATE (Above). 
AGATE CHARMS AS SOLD TO THE NATIVES OF SENEGAL (Below). 


AGATE—ARCHAEOLOGY AND FOLK-LORE 27 


agate,—small pieces of agate cut en cabochon with a 
flattish, circular, or oval back to show the “eye” or 
“eyes.” Nicolo Conti, a Venetian, who travelled in 
India during the first part of the fifteenth century, 
writes that some regions of India have no money, but 
instead use for exchange stones which we call cat’s- 
eyes. 

As is evident from Barbosa’s account, the art of 
coloring agates artificially was partially understood in 
India. At the present time the stones collected near the 
village of Rotanpur near Cambay are classified into 
two sorts,—those that should be baked and those that 
should not be baked. The object of baking the stones 
is to bring out their colors. After exposure to the sun 
or by being baked in a cow-dung fire, light browns be- 
come white, and dark browns deepen into chestnut. Of 
yellows, straw colors become rosy, and orange is in- 
tensified into red; other shades of yellow become pink. 
Pebbles with cloudy shades turn into brightly veined 
stones in red and white. The deeper and the more uni- 
form the color, the greater the value. Again, the larger 
and thicker the stone, the more is it valued. White 
carnelians, when large, thick, even-colored, and free 
from flaws, are precious; yellow and variegated stones 
are worth little. 

Barbosa also mentions at Limodra, or as he calls 
the town Limadura, “much chalcedony, which they 
call babagore; they make beads with it and other 
things which they wear about them.” This is the white 
agate of Cambay, called in Anglo-Indian babagooree, 
from Hindustani babaghuri. It is so called from the 
patron saint or martyr of the district in which the 
mines are located, under whose special protection the 
miners place themselves before descending into the 
shafts. According to tradition, he was a prince of the 
great Ghori dynasty, who was killed in a battle in that 


[ 131 ] 


28 FIELD MUSEUM OF NATURAL HISTORY 


region; but this prince is not known from historical 
records. By command of Akbar, the Moghul emperor, 
grain weights of babaghuri were made to be used in 
weighing. All the weights used at court for weighing 
jewels were made of transparent white agate. 

Agates are much used in India for ornamental 
purposes, being made into brooches, rings, seals, cups, 
and other trinkets. A considerable trade is still car- 
ried on in the raw material which is obtained from the 
amygdaloidal flows of the Deccan trap, chiefly from 
the State of Rajpipla, where the main source is a con- 
glomerate near the village of Ratanpur. Here the right 
to collect the stones is leased for a period of five years 
at an annual rental. Aside from Cambay, which is the 
most important place for cutting agate, this industry 
is also carried on at Jabbalpur (or Jubbulpore) and a 
few other places within range of the Deccan trap. 
Much of the agate sold in Europe is exported from 
Cambay, and large quantities are also shipped to 
China. 

The French traveller and gem-merchant, Jean 
Baptiste Tavernier (1605-89), mentions the beautiful 
agates cut at Cambay into cups, knife-handles, beads, 
and other objects. 

Moss agates were formerly known also as tree- 
stones (French agates arborisées). John Fryer, who 
travelled in India and Persia from 1672 to 1681, de- 
scribes the precious stones found in India in his time, 
among these tree-stones with the lively representation 
or form of a tree thereon. 

It was a wide-spread belief among the Moham- 
medans of India that agate had the power of stopping 
the flow of blood, presumably because of its blood-red 
color. The white carnelian was regarded as a ‘“milk- 
stone,” and was beneficial to women in increasing their 
supply of milk. 


[ 132] 


AGATE—ARCHAEOLOGY AND FOLK-LORE 29 


It is curious that agate is not referred to in ancient 
Sanskrit literature, either in medical texts or in mine- 
ralogical treatises. On the other hand, great quanti- 
ties of agate objects have been discovered on very 
ancient archaeological sites of southern India, not only 
in the shape of beads, but also in the form of cores, 
flakes, scrapers, and strike-a-lights; numerous color 
varieties like white, gray, red and white, brown and 
gray, banded gray, deep red, dull red, orange-red, etc., 
are represented among these antiquities. It may hence 
be inferred that the ancient aboriginal inhabitants of 
India were well acquainted with the stone and utilized 
it for every-day implements in times anterior to the 
Aryan conquest and that the Aryan invaders learned 
its use and adopted it from the aborigines. 

Agate is appreciated by the Tibetans, and is used 
to some extent, though not so largely as turquois, coral, 
and amber, their favorite jewels. It is partially im- 
ported from India, partially from China, and some is 
found in the country itself. Large pieces of red agate 
attached to cloth are worn by the Panaka women in 
the Kukunor region in their hair which is plaited in 
numerous small braids falling over their shoulders. 
Agate is frequently used by the Tibetans in finger- 
rings (examples in Case 61, West Gallery). 

Ancient agate beads, rings, and seals were dis- 
covered by Sir Aurel Stein at Khotan and other locali- 
ties of Chinese Turkestan; also an intaglio of agate 
with the figure of a lion. 

The ancient Chinese herbalists and Taoist doctors, 
who were chiefly interested in the healing properties 
of organic and inorganic substances, classified agate as 
a species of its own. Under this term, which is ma-nao 
in their language, they included also carnelian. Their 
definition of ma-nao is formulated to the effect that it 
is neither a common stone nor jade, but that it holds 


[ 183 ] 


30 FIELD MuSEUM OF NATURAL HISTORY 


a rank inferior, but next to their highly prized jade. 
Agate, accordingly, was appreciated, though not the 
equal of jade and not like the latter a sacred substance. 
It was recognized as a hard stone, being capable of 
resisting cutting instruments. Red, white, and black 
varieties were distinguished. Those which after carv- 
ing and polishing offered pictures of. men, animals, 
birds, or objects were most highly esteemed. In 
southern China a kind of agate of a pure red and with- 
out veins was found; it was made into cups and vases. 
A dark green variety was obtained in the northwestern 
parts of the country. Moss agate is designated 
“eypress-branch agate,” also ‘“nettle-hemp agate’; 
undulated agate, “cloud agate.” Other terms like 
“brocade-red agate, silk-thread agate, rice-water 
agate” refer merely to color varieties. “Lampwick 
agate” is a variety with white veins. “Dark-like-gall 
agate” is what we call bloodstone. “Bamboo-leaf 
agate” came from Yi-chou in Shan-tung Province, and 
was used for inlaying in screens and tables; as implied 
by the name, it displays designs like bamboo leaves. 
The same locality produced another kind termed “jade 
agate.” 

Chinese authors speak of a kind of agate that is 
brilliant white of color if looked at straight, but that 
appears like coagulated blood if looked at from the 
side. It was called “double foetus agate” (kia t‘ai ma- 
nao). ‘“Purple-cloud agate” was found at Ho-chou in 
An-hui Province. 

The ancient Chinese conceived the origin of sev- 
eral stones and salts as marvelous transformations 
from other substances; thus, white rock-crystal was 
believed to be thousand years old water changed into 
ice. By a similar process of naive reasoning agate was 
interpreted as a transformation of the blood of the 
manes or departed spirits, also of malignant devils. 


[ 134] 


LEAFLET 8, PLATE XIll. 
baad 
\ 


NECKLACE OF AGATE, LAPIS LAZULI AND GOLD. 


About 3000 B. C. From Excavations at Kish by Field Museum-Oxford University 
Joint Expedition (Capt. Marshall Field Fund). 


AGATE—ARCHAEOLOGY AND FOLK-LORE 31 


Another theory was based on the name for agate, 
ma-nao, which means literally “horse’s-brain.” In 
writing the two characters, each is usually preceded by 
the classifier “jewel” or “precious stone.” The signifi- 
cance “horse’s brain’ is regarded by most Chinese 
authors as the origin of the word, and may have been 
elicited by a certain outward resemblance of the veins 
and striation in agate with the brain of a horse. Hence 
a popular notion arose that agate beads were spit out 
of the mouths of horses. 

For the purpose of testing agate the following 
recipe is given: “Rub it with a piece of wood; if it 
does not become heated, it is genuine; if it will be 
heated, it is not genuine.” This test is based on the 
notion that the nature of agate is cold and that its 
coldness is unchangeable. The Chinese formula is 
practically identical with what Pliny ascribes to Per- 
sia: there the efficacy of an agate was determined by 
throwing it into a cauldron of boiling water and turn- 
ing the water cold. It may be that the Chinese derived 
this idea from Persia. 

In the first centuries of our era the Chinese be- 
came acquainted with the fact that agate and many 
other valuable stones were abundant in the Near East. 
As numerous articles were then traded from the Hel- 
lenistic Orient to India and China, while Chinese silk 
found its way to the West, it is very probable that 
agate was included among the export products of 
western Asia. 

It is even possible that agate first became known 
to the ancient Chinese as an importation from abroad, 
for it is not mentioned in the literature of pre- 
Christian times, and the earlier authors inform us that 
it came from western countries, from the countries in 
the south-west, or from the western and southern bar- 
barians. In one source it is even stated that it was a 


[ 135 ] 


32 FIELD MUSEUM OF NATURAL HISTORY 


product of the country of the Yiie-chi, known to us as 
the Indo-Scythians. A tribute of agate was sent from 
Samarkand to the Chinese Court in the beginning of 
the eighth century. It is specifically asserted that 
agate was imported into China by the Arabs, but this 
product in all probability was carnelian, as it is de- 
scribed as “standard red in color without flaw.” It 
was the raw material which was imported and which 
was wrought into objects by the Chinese. Subse- 
quently, however, agate was discovered by them in 
many localities of their country, especially near Ning- 
hia, Kwa-chou, and Sha-chou in Kan-su Province and 
in the outlying deserts, also in some mountains of 
northern Shan-si, Chi-li, and Shan-tung. 

Toward the end of the Ming dynasty, in the first 
part of the seventeenth century, as we learn from a 
Chinese cyclopaedia completed in 1632, agate was im- 
ported into China from Europe; this became known 
as “foreign agate.” That of red color was most highly 
appreciated; in its interior it displayed branches of 
cypresses and veins of various colors, as fine as silk 
threads; a variety with white veins was regarded as 
superior. Soon afterwards the same stone was dis- 
covered in Ytin-nan, and was termed “native agate.” 
The Ai-lao Mountains in the prefecture of Yung- 
ch‘ang of that province enjoy a special reputation for 
their agates. Agate was also imported into China from 
Japan in three varieties—red, black, and white. As 
stated above, rough agates are exported from India to 
China in considerable quantities, particularly to Canton. 

Small flat disks of red agate, usually covered under 
the surface with fine white lines of clayish origin, have 
been found in graves of the Han period (206 B.C.-A.D. 
220). There are several early records of wine-vessels 
of agate having been discovered in tombs. Horse’s- 
bits of agate are also mentioned. Large agate beads of 


[ 136 ] 


AGATE—ARCHAEOLOGY AND FOLK-LORE 83 


circular and cylindrical shapes, rings and bangles, as 
well as small disks of translucent moss agate are 
traceable in graves of the T‘ang (A.D. 618-906) and 
later periods. An ancient necklace or rosary found in 
a grave of Shen-si Province and shown in Case 38, 
East Gallery, consists of beads carved from agate, 
lapis lazuli, jade, and jujube-stones. 

In A.D. 662 a tree three feet high made of agate 
in the shape of a lamp was sent by the country To- 
khara as a gift to the Chinese emperor. The branches 
of this agate tree were presumably fashioned in such 
a manner that they could hold an oil-lamp or candle. 
In more recent times jade trees were made by the 
Chinese as wedding gifts. In many of these leaves and 
flowers are carved from jade, but agate and carnelian 
are much used for the petals of the blossoms, as may 
be seen in a good example of the Blackstone Chinese 
Collection (Case 1). A paper-weight of white and red 
agate in which eight lizard-shaped dragons are carved 
is on view in the same case. 

Formerly agate was also wrought in China into 
hair-pins, fish-hooks, and chessmen; and large slabs 
were used for desk-screens and table tops. The art- 
loving emperors of the Sung dynasty (A.D. 960-1278) 
had a high appreciation of agate. In A.D. 1115 some 
large agate blocks were found and transported into 
the imperial atelier, where they were wrought into 
precious objects like vases and ornamental plaques for 
girdles which were preserved in the imperial treasury 
for more than a century. Finally the colors are said 
to have faded away, and the stones assumed the color 
of white bone, whereupon the objects were discarded 
and disposed of to the people. In A.D. 1272 the Mongol 
emperors established in their capital Ta-tu and other 
places an “Agate Bureau” in charge of a director who 
supervised five hundred workmen. 


[ 137] 


34 FIELD MUSEUM OF NATURAL HISTORY 


In the fourteenth century there were made finger- 
rings inlaid with a piece of agate in which were en- 
graved the twelve horary characters corresponding to 
the twelve signs of the zodiac. A contemporary author 
describes the work of engraving as fine as hair and 
conveying the impression as though it were not an arti- 
fact of man; it was therefore styled “devil’s work 
stone” or “stone of the devil’s country.” 

Powdered agate is said to have been used together 
with copper oxide and other ingredients in the produc- 
tion of a red glaze on porcelains. 

The great force of the Chinese lapidary is the 
carving of snuff-bottles in which he strives at bringing 
out the colors of the stone to best advantage, or cuts 
the designs in layers so that the different colors stand 
out in relief as in antique cameo-work (Plate XIV, 
Fig. 3). Agate snuff-bottles are on view in the case 
illustrating the use of tobacco in China (south end of 
West Gallery). Some of these are reproduced in Leaflet 
18 of the Department of Anthropology (Plates VIII 
and IX). The sentiment attached to the gift of a snuff- 
bottle of moss agate is that it should be a disperser of 
melancholy. 

During the K‘ien-lung period (1736-95) and some- 
what later fine agate carvings were also made to be 
worn as pendants in the girdle. Three such ornaments 
are illustrated in Plate XIV, Figs. 1-2 and 6. The 
pendant in Fig. 1 represents a carp with lotus leaves; 
that is, the carp is conceived as swimming in a lotus 
pond. That in Fig. 2 shows a bird with a fruit, leaves, 
and blossom. That in Fig. 6 is carved into three ju- 
jubes (Zizyphus vulgaris) with two small peanuts 
(only one is visible in the illustration). The snuff- 
bottle in Fig. 3 is of milk-white agate with relief carv- 
ings in black, brown, and yellowish layers. These rep- 
resent two monkeys, a spotted deer (Cervus manda- 


[ 138 ] 


EEAFLET-8. PLATE XIV. 


5 6 


AGATE ORNAMENTS AND SNUFF-BOTTLES, CHINA. 
1-2, 6, GIRDLE PENDANTS; 5, RING OF MOSS AGATE. 
Capt. Marshall Field Expedition to China, 1923. 

3-4, SNUFF-BOTTLES. 

From the Collection of Mrs. George T. Smith, Chicago. 


AGATE—ARCHAEOLOGY AND FOLK-LORE 35 


vinus), and a magpie flying into the open from a pine- 
tree. Fig. 4 is a plain agate bottle of various colors, 
brown in the upper portion and green in the lower 
one. Fig. 5 is a ring of moss agate, 134, inches in 
diameter. 

Agate was traded by the Chinese to their neigh- 
bors, the Tibetans, Mongols, Manchu, and Japanese, 
all of whom have adopted their word ma-nao (in Japa- 
nese meno). The Japanese, like the Chinese, manu- 
facture agate and carnelian into beads for rosaries, 
paper-weights, ink-stones for rubbing the cakes of 
ink on, fruits, buttons, seals, tea and wine cups, and 
in particular into the small ornaments known as 
netsuke. 


It is known in Japan that agate becomes more 
opaque on being exposed to sunlight or subjected to an 
intense heat in a closed jar, but the methods of color- 
ing agate artificially, as employed in Europe, were un- 
known both in China and Japan. 

The agate found in the province of Kaga was re- 
garded as very precious. A red variety of it was called 
“‘vine-grape stone,” and served for plaques to be inlaid 
in girdies in the place of jade. The provinces Mutsu, 
Echiu, Suruga, and Kai have the highest reputation 
for their agates and the skill of their lapidaries. Agate 
was formerly also imported into Japan from China. 


Agate, being found in numerous localities of 
America, attracted the attention of the aboriginal in- 
habitants at an early date. In North America and 
Mexico agate was wrought into arrow-heads and spear- 
heads. A beautiful agate spear-head, for instance, was 
found in one of the Hopewell mounds of Ohio. The 
Museum has numerous agate beads recovered from 
prehistoric graves of Colombia, South America. 


B. LAUFER. 


[ 139 ] 


Additional information about Agate can be ob- 
tained from the following works: 


LIESEGANG, RAPHAEL Ep.—Die Achate. Theodor Steinkopf, 
Dresden and Leipzig, 1915. 118 pp. 


DREHER, O.—Das Farben des Achates. 


E. Kessler, Idar, 1918. 
20 pp. 


BavurerR, Max.—Precious Stones. Translated with additions by 


L. J. Spencer. Griffin and Company, Ltd. London, 
1904. 627 pp. 


KuNz, GEORGE F.—Gems and Precious Stones of North America. 
Scientific Publishing Company, New York, 1890. 336 pp. 


The Magic of Jewels and Charms. J. B. Lippincott Co., 
Philadelphia. 1915. 422 pp. 


[ 140 J 


PRINTED IN THE UNITED STATES OF AMERIC 
BY FIELD MUSEUM PRESS 


